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Old 3rd September 2011, 07:07 AM   #11
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A few more of the heart and soul of the amp!
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Old 3rd September 2011, 10:24 AM   #12
AndrewT is offline AndrewT  Scotland
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Due to the way the "I" section is rolled/extruded, you must ensure that the area of the output device mounting interface is FLAT. If it's not FLAT then it will result in poor thermal performance.
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Old 3rd September 2011, 05:00 PM   #13
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Another "area of interest"--the primary radiating surface of the heatsinks is a considerable distance from the heat sources (semiconductors). This can really reduce the efficiency of the heatsinks in cooling the MOSFETs. Best to very carefully monitor your MOSFET temps as you bias them.

In addition, since the I-beam is bolted to each heatsink in only two places (or so it appears), you have to watch the thermal conductivity at the surface of the I-beam to the surface of the heatsinks--both mating surfaces should be very flat, and more fasteners would help--and some thermal grease might be useful. (Whenever I'm are concerned about thermal mating, I'll use a milling machine on both mating surfaces to get a true flat surface......either that, or lap them in with a valve grinding slurry, and a piece of thick glass as a "truing surface")
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Old 3rd September 2011, 05:06 PM   #14
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I absolutely agree Andrew, a few years ago I got some heatsinks that came with a cheap stereo amp kit. After the outputs on one channel blew I discovered the heatsink mounting surfaces weren't flat, resulting in fried transistors. I had them milled flat at a machine shop in the area and the problem was solved. Ironically, the milling service cost nearly as much as the amp kits.

Mike
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Old 3rd September 2011, 05:42 PM   #15
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You can do a good job lapping a sink, by just glueing a sheet of very fine waterpaper to a mirror or piece of glass to give you a flat surface to grind it on. Not that it would work for this unusual configuration.
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Old 3rd September 2011, 06:27 PM   #16
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I am watching all of these things. I am going to prep each sink and the I-beam to get a good contact. I will also watch temp on device, at device I-beam junction, and at the heatsinks.

I think I will be ok. The test run did not show any spots I should be alarmed about.
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Old 3rd September 2011, 11:14 PM   #17
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CanAm Man got it right
Remind me of my prentice days hand lapping 130Hp Volvo Penta heads
IF I may
I did hand lapping on my sinks and heath spreaders.

By hand lapping I mean rub one against the other in small circles on the place where they are meant to sit

I started with emery paper on a granite surface to get them flat then spreaders against sinks I had a spare granite tile so no risk of breaking mirrors and such which still vuld work fine.

As you have many small sinks this shuld work well.

Once most of the 600-grain paper scratches where of with fine carbide I started using varnish scratch remover and baking soda or tooth paste work fine as well

You may notice how mirror like one spreader look next to the other

After about 10 hours and having cleaned the lot a few times the heat spreader where sticking to the sinks as if magnetized (Yea I know cooper and aluminium do not get magnetized but that is how it felt like) maybe same professor here would care to explain.

To complete the assembly I used graphite heat sink grease at 10W/mK is about 3 times than the best silicon grease.
Farnell PNO is 1315296
This grease is conductive so no good for the mosfets for which I use Keratherm 86/83.

I must say your build looks really good but if you need to improve on the thermal load
Why not having it anodised

They may even do the lot all bolted togheter
Normally they charge a flat fee no matter what quantity you have and eficency of the sink is much better (I am not going to post numbers that you can find on Wikipedia)
While there you can wikipediaup Graphene there is a bit that mention Scotch tape method it works fine with Mica as well
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Last edited by Bksabath; 3rd September 2011 at 11:35 PM.
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Old 4th September 2011, 12:22 AM   #18
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Default re: Toroid Transformer mounting

Quote:
ThorstenL: I learned things I NEVER wanted to about how magnetic fields behave . . .
Below shows several plies of 16 gauge steel used to enclose a torroid and chokes. Top covers removed. (Not quite done with this, yet.)
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Last edited by johnferrier; 4th September 2011 at 12:44 AM.
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Old 4th September 2011, 01:58 AM   #19
sippy is offline sippy  United Kingdom
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Hi Bksabath,
your mirror laped finnish is what keeps the spreader and sink together - its flat enough to displace the air betwixt the two parts and form a vaccume 'bond', much like joey blocks doo in a tool room
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Old 4th September 2011, 07:31 AM   #20
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Tanks sippy

Coupling and heath transfer gotta be good then.

Temperature mesured on tab of a FQP19N20 (TO220) 55.5 sinks at 42 C

I have at present 26 V rails and bias set at 2.8 A

Thermal load on sinks about 145 W for the 4 mosfets (2 on each rail)

Apart from meter capable all you need is a PT100 probe the 1 I use is 1.2 X 2.4 mm, perfect for tight spaces, conected to grey cable on picture 1
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